1. Field of the Invention
The present invention relates to a sheet handling device, and more particularly, to a sheet handling device adapted to align and fasten ejected sheets having images formed on the surfaces thereof by an image forming apparatus, such as a copying machine or a laser beam printer, and in particular, to collect sheets into a stack and effectively align the stack of sheets by an aligning means in a sheet aligning operation. The present invention also relates to an image forming apparatus having the sheet handling device.
2. Description of the Related Art
Hitherto, numerous image forming apparatuses have been proposed, for example, in Japanese Laid-Open Patent Application No. 2-144370, which are equipped with a first handling means (hereinafter referred to as a "handling tray") for aligning and collecting sheets having images thereon into a stack and for stapling a part of the sheet stack as necessary, and a second handling means (hereinafter referred to as a "stack tray") for receiving and holding sheet stacks which have been aligned or stapled.
FIG. 34 schematically shows the configuration of an aligning section in this kind of conventional sheet handling device.
Referring to FIG. 34, the conventional sheet handling device comprises a pair of feeding rollers 701 consisting of a lower feeding roller 701a and a feeding roller 701b for feeding sheets from a sort path, a handling tray unit 800 for receiving the conveyed sheets, and a stack tray 900 for holding stacks of sheets ejected in stacks after processing.
Knurl belts 702 are wound on the lower feeding roller 701a of the pair of feeding rollers 701 at several positions in the axial direction between the lower feeding roller 701a and the feeding roller 701b. Sheet guides 703 are placed at appropriate positions between the knurl belts 702.
The handling tray unit 800 comprises a handling tray 801 inclined so that the downstream side in the sheet ejecting direction (the upper left side in FIG. 34) is placed on the upper side and the upstream side (the lower right side in FIG. 34) is placed on the lower side, a rear end stopper 802 disposed at the upstream end of the handling tray 801, a pair of aligning members 803 disposed on the right and left sides in the sheet width direction, a pair of stack ejection rollers 804 composed of lower and upper stack ejection rollers 804a and 804b disposed on the downstream side of the handling tray 801, a pivoting guide 805 for supporting the upper stack ejection roller 804b at the leading end on the lower surface so that the upper stack ejection roller 804b can make contact with and separate from the lower stack ejection roller 804a, and a pull-in paddle 806 disposed in the upper middle section.
In this case, the lower and upper stack ejection rollers 804a and 804b are allowed by the control of pivoting of the pivoting guide 805 to receive sheets P from the feeding rollers 701 into the handling tray 801 in the state in which the upper stack ejection roller 804b is separated from the lower stack ejection roller 804a.
The sheets P are continuously pulled back by the rotational driving of the pull-in paddle 806, are aligned by the action of the aligning members 803, and are put into contact with the rear end stopper 802 via the sheet guides 703 by the action of the counterclockwise rotation of the knurl belts 702 for feeding the ends of the sheets, whereby the aligning operation is completed.
Subsequently, the sheets aligned in the handling tray 801 are subjected to stapling or other processes at the aligning position, and are ejected in a stack into the stack tray 900 by putting the upper stack ejection roller 804b into contact with the lower stack ejection roller 804a and rotating the lower stack ejection roller 804a counterclockwise.
In the above-described conventional structure, however, as the number of sheets P stacked in the handling tray 801 increases, the contact pressure of the knurl belts 702 with the sheets P also increases. Therefore, the pulling force toward the rear end stopper 802 increases, whereas an increased resistance is applied to the movement of the aligning members 803 in the aligning direction orthogonal thereto. As shown in FIG. 35, the knurl belts 702 first follow a sheet P.sub.1 moved by the aligning members 803 and are bent and tilted on the nip between the knurl belts 702 and the rollers 701b, but the knurl belts 702 cannot follow further movement of the sheet P.sub.1, whereby slip occurs therebetween. Therefore, when the stiffness of the sheet P.sub.1 is less than the slide resistance, the sheet P.sub.1 is raised, as shown by a broken line Pa (at worst, it is buckled), and does not reach a reference position 803a, which may cause misalignment.